1. Field of the Invention
The present invention is directed to a segmented bottom guide for a string elevator assembly used to handle pipe strings to drill and complete a borehole for recovery of oil or gas. Specifically, the present invention is directed to a segmented bottom guide for directing the top of a tubular member into and through a bore so that the tubular member can be engaged by pipe slips within the string elevator.
2. Background of the Related Art
Wells are drilled to establish a conduit between the surface and a targeted geologic feature such as a hydrocarbon reservoir. Casing strings are made up and installed in the drilled borehole to prevent collapse, cross-flow from one geologic formation to another, and to isolate the interior of the well from corrosive fluids present in some penetrated geologic formations. Generally, a pipe string is suspended in a borehole and lengthened by threadedly joining a pipe segment to the proximal end of the pipe string at the rig. The lengthened pipe string is then lifted to unload the spider that suspends the pipe string, and the lengthened string is lowered further into the borehole. The spider again engages and supports the pipe string as additional pipe segments are joined to farther lengthen the pipe string.
Special tools exist for positioning a pipe segment to be threadedly joined to the proximal end of the suspended pipe string. In one well known method, a pipe segment is secured to a lift line that hoists the pipe segment into the derrick to dangle the lower end of the pipe segment near the proximal end of the pipe string. The lower “pin” end of the pipe segment is positioned by rig personnel to be received into and bear against the proximal “box” end of the pipe string suspended by the spider in the borehole. A “stabber” is a member of the rig crew that works in the derrick. The stabber is secured to the derrick to prevent him from falling as he leans out to manually position the top “box end” of the pipe segment to align it with the pipe string. A power tong may be used to grip and rotate the pipe segment about its axis to make up the threaded connection between the lower “pin end” of the pipe segment and the proximal box end of the pipe string to lengthen the pipe string. The stabber then aligns the top box end of the now-connected pipe segment into the bell guide of the string elevator so that the box end of die pipe segment can be directed into the gripping portion of the string elevator as the string elevator is lowered over the end of the pipe segment. Once the string elevator is lowered enough to engage and grip the upper end of the pipe segment (which is now the new proximal end of the lengthened pipe string), the string elevator lifts the entire pipe string to unload the spider, and then it lowers the pipe string to install the lengthened pipe string further into the borehole.
When the string elevator nears the spider, the spider may reengage and support the pipe string to strategically position the new proximal end of the now-lengthened pipe string above the spider to receive and couple to a new pipe segment. This method of forming and installing a pipe string in a borehole is repeated until the pipe string reaches its desired length.
The string elevator used in the method described above is adapted to receive the proximal end of a lengthened pipe string from below, and to be lowered over the end of the proximal end of the pipe string as it is positioned by the stabber for being received into the elevator. After the proximal end of the pipe string is received into the tapered bowl, it may be releasably gripped using a set of slips that have been moved upwardly and radially outwardly from the center of the tapered bowl to receive the pipe string, and that can be engaged by moving downwardly and radially inwardly within the tapered bowl to engage and grip the pipe string. The proximal end of the pipe string must generally be carefully positioned by the stabber to ensure that it enters the string elevator from beneath as the string elevator is lowered using a drawworks. After the pipe segment is threadedly connected to the exposed proximal end of a pipe string, the pipe string is lengthened, and the new proximal end of the pipe string is positioned high above the rig floor. The proximal end is then guided through the opening in the bottom of the tapered bowl and into the tapered bowl so that the lengthened pipe string can be gripped and then lifted up to unload the spider.
The insertion of the proximal end of the lengthened pipe string into the opening in the bottom of the tapered bowl has to be done at a position far above die rig floor where it is impractical for rig personnel to physically guide the proximal end of the pipe string into the opening in the bottom of the tapered bowl. For this reason, the string elevator is generally provided with structures adapted for guiding the proximal end of the lengthened pipe string into and through the opening so that the proximal end of the pipe string can be gripped by the slips within the tapered bowl. A bell guide is a generally hollow interior conical frustum for receiving and guiding the top end of the lengthened pipe string toward the opening in the tapered bowl of the string elevator.
The bottom guide is a second structure for cooperating with the bell guide in guiding the top end of the pipe string into the opening of the tapered bowl. The bottom guide is secured between the bell guide and the opening in the bottom of the tapered bowl to receive the top end of the pipe string after it leaves the bell guide and to further direct it to the opening. Since most string elevators can be “dressed” or modified using inserts, spacers and sleeves to grip and lift a range of pipe diameters, the diameter of the opening in the bottom of the tapered bowl may vary depending on the diameter of the pipe string being made tip and run into the borehole. For this reason, the bottom guide may be replaceable to enable the use of an appropriately-sized bottom guide for receiving the top end of the pipe string from the top of the bell guide and guiding it to the opening in the tapered bowl. The bottom guide must have the appropriate size and taper for guiding the received top end of the pipe string to the opening.
However, depending on its capacity, the string elevator may weigh up to 15,000 pounds or more. Similarly, the slips, the bell guide and the bottom guide each may weigh hundreds of pounds. Replacing, the heavy bottom guide can be difficult and time consuming, not only because of the weight, but also because the bottom guide is generally positioned between the bell guide and the tapered bowl, and access to the bottom guide often requires removing the bell guide and removing fasteners from underneath the heavy tapered bowl. Once removed from the tapered bowl, the bottom guide may be very heavy and difficult to handle. The bottom guide may require removal of other heavy components, such as the bell guide, to provide access to the bottom guide. For example, one commercially available string elevator requires removal of the heavy slips to replace the bottom guide. Other string elevators require that the string elevator be suspended for replacing the bottom guide, and personnel replacing the bottom guide must work with their hands underneath the suspended string elevator, thereby exposing personnel to potential danger or, at the very least, a difficult working position.
What is needed is a string elevator assembly that provides easier access to the bottom guide so that the bottom guide profile can be adapted to guide the top end of a pipe string from the top of a bell guide to the opening in the bottom of the tapered bowl. What is needed is a string elevator assembly that facilitates the replacement of the bottom guide without exposing rig personnel to unnecessary danger or difficult working positions. What is needed is a more versatile string elevator assembly that includes a bottom guide that can be safely replaced to accommodate a range of pipe diameters.